rebase: allow --merge option to handle patches merged upstream

Enhance t3401-rebase-partial to test with --merge as well as
the standard am -3 strategy.
Signed-off-by: NEric Wong <normalperson@yhbt.net>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-rebase.sh

@@ -82,7 +82,10 @@ call_merge () {
 	rv=$?
 	case "$rv" in
 	0)
-		git-commit -C "$cmt" || die "commit failed: $MRESOLVEMSG"
+		if test -n "`git-diff-index HEAD`"
+		then
+			git-commit -C "$cmt" || die "commit failed: $MRESOLVEMSG"
+		fi
 		;;
 	1)
 		test -d "$GIT_DIR/rr-cache" && git-rerere
@@ -110,9 +113,13 @@ finish_rb_merge () {
 	do
 		git-read-tree `cat "$dotest/cmt.$msgnum.result"`
 		git-checkout-index -q -f -u -a
-		git-commit -C "`cat $dotest/cmt.$msgnum`"
-
-		printf "Committed %0${prec}d" $msgnum
+		if test -n "`git-diff-index HEAD`"
+		then
+			git-commit -C "`cat $dotest/cmt.$msgnum`"
+			printf "Committed %0${prec}d" $msgnum
+		else
+			printf "Already applied: %0${prec}d" $msgnum
+		fi
 		echo ' '`git-rev-list --pretty=oneline -1 HEAD | \
 					sed 's/^[a-f0-9]\+ //'`
 		msgnum=$(($msgnum + 1))

t/t3401-rebase-partial.sh

@@ -37,7 +37,9 @@ test_expect_success \
 test_expect_success \
     'pick top patch from topic branch into master' \
     'git-cherry-pick my-topic-branch^0 &&
-     git-checkout -f my-topic-branch
+     git-checkout -f my-topic-branch &&
+     git-branch master-merge master &&
+     git-branch my-topic-branch-merge my-topic-branch
 '
 
 test_debug \
@@ -50,4 +52,13 @@ test_expect_success \
     'rebase topic branch against new master and check git-am did not get halted' \
     'git-rebase master && test ! -d .dotest'
 
+if test -z "$no_python"
+then
+    test_expect_success \
+	'rebase --merge topic branch that was partially merged upstream' \
+	'git-checkout -f my-topic-branch-merge &&
+	 git-rebase --merge master-merge &&
+	 test ! -d .git/.dotest-merge'
+fi
+
 test_done